I have a problem with my real implementation

I want to create a figure editor but I don't know if the squares of the axes should be Graphics or not, since they will not have all the methods.

I have adapted the diagram from your book in this way:

At the beginning I had this diagram:

I also considered the opportunity to include something like this:

The main problem is that I don't know how to define this, because when the figure on which it is to act rotates or is scaled this figure must also do so.

It is a set of figures? but it is an overlay for the figure that is selected, so it is part of the figure? I don't know how to consider it?
how can I know when an object is part of another object or is an independent object? I have a lot of doubts, sorry.

I hope you will consider the possibility of helping me with this, since in general I have a lot of doubts when designing software.

Thanks for everything, hopefully one day you will write a book that will teach me how to design solutions.